Irony = when the opposite of what is expected happens
Verbal irony - when you mean the opposite of what you say (i.e., "You are sooo nice!" -> someone isn't nice at all)
Situational irony - when the opposite happens of what is expected (i.e., a fire station burns down; the police gets robbed, a pilot is afraid of heights etc.)
Dramatic irony - when the audience/reader knows what will happen & the characters in the play/novel don't (i.e., in detectives, Shakespeare's plays -> you know something is about to happen, the characters don't know this